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(No Model.) 6 Sheets-Sheet 1.

G. P. DURANT, W. W. DEAN 85 W. A. OHILDS. TELEPHONE SYSTEM.

No. 565,968. Patented Aug. 18., 1896.

W1 messes.

'(No Model.) 6 Sheets-Sheet 2. (I

G. P. DURANT, W. W. DEAN & W. A. OH'ILDS. TELEPHONE SYSTEM.

No. 565,998. Patented Aug. 18, 1896.

(No Model.) 6 Sheets-Sheet 3.

G. F. DURANT, W. W. DEAN & W. A. CHILDS. TELEPHONE SYSTEM.

No. 565,968. Patented Aug. 18, 1896.

(No Model.)

6 Sheets-Sheet 4.

G. F. DURANT, W. W'. DEAN 87; W. A. OHIL'DS.

TELEPHONE SYSTEM. No. 565,968. v

Patented Aug. 18, 1896.

Wz'inesses. Jn'mhiof ai M44 (No Model.) k I 6 Sheets-Sheet 5'. G. P.DURANT, W. W. DEAN 8?; W. A. C-HILDS. TELEEHONE SYSTEM.

Patented Aug. 18, 1896.

Fig. 6.

Wzznesses [nwn #02 5.

fif a (No Model.) 7 I r 6 sneei -snep s. G. FpDURANT, W. WQDBAN: 8B W.vA. CHILDS. TELEPHONE SYSTEM.

No. 565,968. Batnted Au 18, 189 6 Witnesses fllfa I 7 ,UNITJED F PATENTOFFICE.

GEORGE F. DURANTiAND WILLIAMiW. DEAN, OF ST. LOUIS, MISSOURI ANnw LIAMA.CHILDS, OF NEW YORK, N. Y., ASSIGNORS TO THE BELL TELEPHONE O MPANY EMISSOURI, OF ST. LOUIS, MISSOURI.

TELEPHONESYSTEM.

SFECIFICATION forming part of Letters Patent No. 565,968, dated August18, 1896.

Application filed April 10, 1896. Serial No. 586,965. (No model.)

To all whom, it may concern.- 5

Be it known that we, GEORGE F. DURANT and ILLIAM V.- DEAN, residing atthe city of St. Louis, in the State of Missouri, and

WILLIAM A. CHILDS, residing at the city of New York, in the State of NewYork, citizens of the United States, have invented certain new anduseful Improvements in Telephone Systems, of which the following is sucha full, clear, and exact description as will enable any one skilled inthe art to which it appertains to make and use the same, reference beinghad to'the accompanying drawings,'

forming part of this specification.

The invention relates to improvements in telephone trunking systemsbetween central oflices, whereby a subscriber at one central office maybe conveniently and expeditiously connected with a subscriber belongingto another central office, and signals given to the.

operators at the two central offices of the con dition of thetrunking-wires.

The invention consists in features and combinations hereinafter setforth, and pointed out in the claims at the end of this specification.

In the accompanying drawings is shown the trunkingsystem applied to atelephone systemknown as the magneto system, but the invention isnotconfined to such system, as it is capable of use with any telephonesystem.

The invention will be best understood by referring to the accompanyingdrawings, which represent diagrammatically one form of the invention.

Figure 1 is a View showing such parts of the apparatus at and connectedwith two central offices as are necessary to illustrate the invention,all the parts in Fig. 1 being represented in their normal positions.Fig. 2 is a similar view to Fig. 1, wherein one of the sub scribers hassignaled to one of the central oflices, the Operator at which office hasconnected the terminals of such subscriber with the terminals at one endof the trunking system. Fig. 3 is a View similar to Fig. 2, but showingonly the apparatus at and connected with the central office at thereceiving end of the .trunking system, and illustrating the position ofthe parts when the operator at said central oflice has plugged in uponthe receiving-terminals of the trunking system in response to the signalsent her by the centraloffice operator at the sending end of thetrunking system, plugging in upon the trunking system, and showing thelistening-key of c the receiving-operator connected with saidreceiving-terminal pushed down, thus placing trunking system has pluggedin upon the terminals of the subscriber wanted, the ringingkey of thereceiving-operator, connected with the terminals of the subscriberwanted, being I pushed down to ring up the subscriber wanted. Fig. 5 isa View similar to Fig. 2 after the connections have been made, as inFigs. 3 and 4, and showing that the subscriber wanted has responded, histelephone-hook being up, and the two subscribers are conversing over theconnections made and the trunking system.

Fig. 6 is a view similar to Fig. 5, except that the calling subscriber,being through talking, his telephone-hook is down, which fact hav ingbecome known to the central-office Operator at the sending end of thetrunking system, said Operator has disconnected her switch-plug from theterminals of the calling subscriber and from the terminals of thetrunking system. Fig. 7 is a view similar to Fig. 6, except that thesubscriber wanted is represented as being through talking, histelephone-hookbeing down, whereupon the centralofiice operator at thereceiving end of the trunking system has disconnected her switchplugsfrom the terminals of the lines of such subscriber and from theterminals of the trunking system and has pressed a signaling key tosignal the operator at the other central office. a 1

The same marks of reference indicate the same parts in the severalviews.

' A represents the calling subscriber, and B the subscriber wanted; 0,the central Office connected with the calling subscriber and at theSending end of the trunking system, and O the central office connectedwith the sub-..

scriber wanted and at the receiving end of the trunking system.

T represents the trunking system between the two central offices.

Z are the line-wires emanating from subscribers to the central office.These lines each terminate at the central offices in a spring-jack. Eachsubscriber is provided with the usual telephonic appliances, including amicrophone-transmitter 14:, arranged in the ordinary way. Theseappliances need not therefore be particularly referredto.

t t are trunk-wires leading from the central office 0 to the centraloi'iice 0 They are represented by full heavy lines. At the sending endof these trunk-wires are a series of multiple-board connections orspring-terminals 25, arranged in sets of two. There are as manytrunk-wires as are necessary to transact the business between any twocentral offices, each set of trunk-wires having a series of terminals25. Above the terminals 25 are arranged terminals 26 of a wire 27. Thiswire 27 branches into a wire 28,- which contains in its path anelectromagnet 29. The wire 28 passes to a wire 30, between which and awire 31 is arranged in multiple are a series of incandescent lamps 32,or other signaling devices, one of said lamps being allotted to eachsection of the multiple board, and represented in the drawings aslocated just beneath each set of terminals 25 and 26. From the wire 31proceeds a conductor 33 to the armature 34 of a relay 35. This armatureis normally held in position against its back contact by a spring 30. Inelectrical communication with the armature 3a of the relay 35 is aline-wire 37, (shown by a broken line,) which is connected at each sidewith the trunk wires 15 25, so that the resistance at each side thereofis equal. The line-wire 37 is in communication with the armature 38 ofthe magnet 29. This armature 38 plays between two contacts, the frontoneof which is in electrical communication through the relay 35 with theground Gr, and the back one of which is in communication with a wire 39,leading to ground by way of a battery 40. The front contact of the relay35 is in electrical communication with the battery 40. Connecting thewires 28 and 30 with the ground is a wire 41, containing in its circuita battery 42.

At the receiving end of the trunking-wires 1525 (central office 0 isarranged a set of spring terminals 45, the same as the terminals 25 atthe sending end of the trunking-wires. Above these terminals is arrangeda terminal 46, which is connected with a conductor 47, con tainingwithin its circuit a magnet 48, connect-ed to the front contact of thesaid relay 4.). The back contact of the said relay 49 is in electricalcommunication with a wire 50, leading to a contact 51, which normally isin contact with a spring 5 2, that is connected to but insulated fromone of the springs of the spring-terminals 4:5. The spring-contact 52leads, by way ofa wire 53,-to the armature of the relay a9, and embraceswithin its circuit a battery 54: and an incandescent lamp 55 or othersignaling device. The armature of the relay 49 is furnished withaspring,.so that when the said relay is deenergized itwill be thrown bysaid spring against its back contact.

Connected to the wire 47 at a point between the magnet 48 and the frontcontact of the relay 49 is a conductor 56, the circuit of which is madeand broken by the armature of the magnet 48 by making contact with itsfront contact, the said armature being held in its normal positionagainst its back stop by a spring. The other end of this circuit 56 isconnected through the incandescent lamp 55 or other signaling device andthe battery 54 to earth.

The relay 4:9 is in the circuit of a line-wire 57, (shown by a brokenline,) which is connected at one end to ground and at each side of theother end to the trunking-wires 2' t, the resistance at each side ofthat end of the line wire 57 being equal. From that end of the linewire57 connected between the trunk-wires t t is a conductor 58, leading to akey 59.

85 is a conductor, one end of which is connected in front of the battery54: and the other end of which terminates in cooperative proximity tothe key 59.

If the central office 0 wishes to have the central office 0 connect oneof C subscribers with a subscriber belonging to central office C, theconnections in that case are made over a different set oftrunking-wires, and for this purpose the central office (1 is providedwith a sending trunking apparatus like the central office C, and thecentral office O with a receiving trunking apparatus like the centraloffice 0 As many sending and receiving trunking apparatus arerespectively provided for the different central offices as may benecessary to transact the business between the two offices.

Ilaving described the apparatus at the subscribers stations, and alsothe construction and arrangement of a trunking system made after theinvention, the devices whereby communication is established betweensubscribers and the trunking system will now be explained. Normally inthe circuit of each of the line-wires Z at each central station is theusual indicator 1. P and P are plugs at central office 0 by whichconnections are made, and P and l?" plugs at central ofiice C for thesame purpose. These plugs 'are all alike. Each consists of a terminalknob 63 and two contacts (35 and 67. They are connected together in setsof two. At the central station G the terminal knobs 63 of a set areconnected together by a wire 64, the contacts (35 of a set beinglikewiseconnected together by a wire 68, and the contacts 67 by a wire 66, whichis suitably grounded. In a derived circuit from the wires 64 and 68 isarranged central-office operators (O) talking I and listening key K,whichis adapted to put in circuit her microplione-transmitter andherthereof will now be explained.

' indicator 1', as'illustrated in Fig. 2.

head telephone-receiver. In a derivedfcircuit from the wires 64 andI68at central office 0- is also an operators indicator of the ordinarykind. v At central office 0 the arrangement of the plugconnections isslightly'different, because:

66. The terminal knob -63 of the plug P is in communication by wayof-wire 64 with one of the back contacts of ringing-key K the other backcontact'thereof being in electrical connection with contact 65 of plug Pvia wire 68. The terminal knob 63 and contact 65 of plug P arerespectively connected to the spring-terminals of the ringing-key K Inderived circuits across the-wires 64 and 68 is an operators talking andlistening'key K, the same as before referred to, as well as an operatorsindicator. puts to the subscribers lines the current generated by asmallmagneto-machine S6.

Having fully set forth theconstruction and arrangement of the apparatus,the operation In Fig. 1 is shown 'the normal position of all parts. Inthe trunking system the battery 40 is normally to the trunking-finest tby wayof armature 38 of themagnet29' and the wire 37 The current afterleaving the trunking wires passes over the conductor 57' throughtherelay 49 to' ground, and by way of the ground returns to the otherpole of the battery 40. This draws upward the armature of the relay 49against its front contact. Normally the lights 32 are out at the sendingend of the trunking system, as well as the light 55 at the receiving endof the trunking system, as shown in Fig. 1. Let us suppose thatsubscriber A in Fig. 1 has removed his telephone from its hook andthereby signaled the central-oirice operator 0 by means of his Thecentral-oifice operator 0 now plugs in upon the terminals of thesubscriber A with her switch-plug, as shown in Fig. 2, and thesubscriber A advises the operator of the number of the subscriberwanted. Let us suppose that the subscriber wanted belongs to anothercentral office, say central office C The central-ofiice operator 0 thenplugs in upon a set of the terminals and 26 of the trunking system, asillustrated in Fig. 2. This completes the circuit of the groundedbattery 42 via wire 30 by way of incandescent lamps 32, wire 31,armature 34 of relay 35, to wire 27, to terminal 26, to switch-plugcontact 67,

to cord 66, and returning by way of ground to the other poleof thebattery 42. This lights the incandescent lamps 32, and serves to therebywarn the other operators at central office 0 that that trunking-circuitis in use and must not be plugged in upon, but

The ringing-key K candesc'ent lamps 32 are not lighted, if any there be,are to be used.

I The current from the battery 42, passing to the wire 30, reaches thewire 28 and divides, part going through said'wire 28 and vitalizing themagnet 29, and after traversing said magnet and circuit 28is reunited tothe other part of the current on the wire 27 j and pursues the coursehereinbefore outlined.

. The magnet 29 in becoming vitalized draws up its armature 38, breakingthecontact with its back contact in communication with the battery. 40.Thistakes said battery 40 off the trunk-wires and grounded conductor 57at the receiving end of the trunking system, which permits the armatureof the relay 49 to be drawn down by its spring against its back contact,Fig. 2. This closes the circuit of the battery 54 through theincandescent lamp 55 by way 'of the following local circuit: frombattery 54 to lamp 55, to armature of the relay 49, to conductor50, tocontact'51, to spring-52 ,and returning to battery,which causes theincandescent lamp 55 to be lighted.

The operator at the central office 0 Seeing the lamp 55 lighted, knowsthat a connection is desired, and plugs in with one of her switchplugsupon the terminals and 46, as shown in Fig. 3. The insertion of thisplug forces back the spring 52 and breaks the circuit of the lamp 55,which has just been tracedbetween the contacts 51 and 52, and the lampis extinguished. The operator at the central office 0 then pushesdow'n'her listening-key .K, connected with the plug which is inserted.erator at the receiving end. Thus it will be seen that the twooperators may, by suitably manipulating their talking and listeningkeys,converse with each'other. The operator O at the receiving'end of thetrunking system, after having plugged in upon the ter-' minals of thetrunking system and suitably manipulated her talking and listening key,as stated, says to central-office operator 0, WVhat number?Central-office operator 0 now advises central-office operator 0 of thenumber of the subscriber wanted. The central office operator 0 thenplugs in upon the terminals of the subscriber wanted with her otherswitch-plug P, as shown in Fig. 4.

7 Centraloffice operator 0 after having plugged in upon the terminals ofthe sub sc'riber wanted, pushes down her ringing-key K Fig. 4. This putsthe generator 86 to lineIand rings the call-bell of the subscriber thatother trunking-wires in whichthe inwanted. The circuit over which thetwo subscribers converse, after being connected together by thecentral-office operator through the trunking system, Fig. 5 is asfollows: from telephone-transmitter 14 of subscriber A, to telephonehook, to line-wire Z of said subscriber connected with said hook, tocontact 63 of the switch-plug P, inserted in the terminals of saidline-wire, to cord 64 of plug P, to cord 64 of plug P to contact 63 ofplug P to the upper trunk-wire t, to contact of plug P inserted in theterminals of the trunk-wires at the receiving end, to cord-conductor 64of plug P via back contact of key K to cord 68 of plug P to contact 65of plug P inserted in the terminal of the subscriber wanted, one of theline-wires Z, by way of telephone-hook of subscriber B wanted, to histelephone-receiver, to other line-wire Z, to contact 63 of plug P tocord 64 via back contact to key K to cord 68 of plug P to contact 65 ofplug P to lower trunk-line i of the trunking system, to contact 65 ofthe plug P to cord 68 of plug P to cord 68 of plug P, to contact 65 ofplug P, to other line-wire Z of the calling subscriber A and histelephone-receiver, thus completing the circuit.

It will be noted that the telephone apparatus of the central-officeoperators are not in circuit during the time that the subscribers areconversing.

/ Let us suppose that the calling subscriber A is the first one toindicate to the central office by means of a clearing-out indicator thathe is through talking and wishes to be disconnected. The central-officeoperator 0 then immediately disconnects said subscriber by withdrawingboth of the switch-plugs P and P as shown in Fig. 6. This breaks thecircuit of the battery 42 through the incandescent lamps 32 and throughthe magnet 29 between the conductor 27 and switch-plugs and puts out theincandescent lamps 32, indicating to the other operators C that this setof trunk-lines is not now in use, and also permits the armature of themagnet 29 to be drawn by its spring against its back contact, as shownin Fig. 6. The battery 40 now passes to the trunk-wires by way of thearmature 38 and line-wire 37, as shown in Figs. 1 and 6, and asheretofore explained. The current from battery 40, after traversing thetrunkwires t t, goes to the conductor 57 through the relay 49 to ground.This, as explained with reference to Fig. 1, draws up the armature ofthe relay 49 from the position shown in Fig. 5 to the position shown inFig. 6 and closes the circuit of the battery 54 through the incandescentlamp 55 by Way of the armature of the relay 49, the wire 47, theterminal 46, connected therewith, the contact 67 of the switch-plug P toconductor 66, to ground, to other pole of battery 54. Within thiscircuit is also embraced the coils of the magnet 48, which is energizedby the current passing around its coils, and draws up its armature andcompletes the circuit of the battery 54 through the incandescent lamp 55, independently of the circuit, by way of the armature of the polarizedrelay, the circuit referred to being from the battery 54 through theincandescent lamp, through the wire 58, to the armature of the magnet48, to the wire 56, to the conductor 47, terminal 46, contact 67 of theswitch-plug P conductor 66, to ground, back to the battery 54. Thislatter-mentioned circuit remains closed independent of the position ofthe armature of the relay 49, but can only be closed by the armature ofthe re lay 49 in the first instance. The lamp 55is therefore lighted andremains lighted. This is a signal to the central-ofiice operator C todisconnect her switch-plug, it meaning to her that the central-officeoperator 0 has withdrawn her switch-plug. Switch-plug in at thereceiving end and lamp lighted means Disconnect. This signal should notbe confounded with the signal, Switch-plug out at the receiving endandlamp lighted, as heretofore explained, which latter signal meansConnect.

The object of having the circuit of the incandescent lamp 55 and itsbattery 54 maintained closed after being closed by the armature of thepolarized relay 49 is to prevent a false signal being given. Forinstance, suppose that after the central-office operator 0 haddisconnected her switch-plug another operator at the central oflice O,seeing the incandescent lamps 32 at the central office C extinguished,should plug in upon theterminals of these trunk-wires before theoperator 0 at the receiving end of these trunk-wires had disconnectedher switch-plug from these trunk-wires. This, as heretofore explained,would energize the magnet 29 and. take the battery 40 off thetrunk-lines, as heretofore explained (see Figs. 2 and 3) and allow thearmature of the relay 49 to drop to its lower position. Thus the circuitof the battery 54 through the incandescent lamp would be broken by thearmature of the relay 49 and by the contacts 51 and 52, and the lamp 55would be extinguished. office operator 0 happened to be attending tosome other matters and looked away from the lamp 55 in the meantime, anddid not see that the lamp 55 had been lighted and extinguished again,but found it extinguished, she would naturally suppose that it hadremained extinguished all the While and that the firstmentionedcentral-office operator 0'' still had her switch-plug connected to thetrunking system, and that the two subscribers were still conversing, forthe signal, Light out and switch-plug inserted at the receiving end,means Do not disconnect. The centraloffice operator 0 would thereforeleave her switch-plug connected with the trunk-wires, whereas aconnection with another subscriber would now be desired. To prevent thisfalse signal, the magnet 48 is employed to maintain the circuit of thebattery 54 through the lamp 55, so that if the central-office operator 0If now the centraldisconnects her switch-plug and, before thecentral-office operator has disconnected, another operator plugs in uponthe trunking: terminals at the sending-ofiiceC, the lamp 55 willnevertheless stay lighted and signal the central-oifice operator C todisconnect.

If the lamp 55 does not g6 out when the operator 0 withdraws herswitch-plug, this indicates to the central-office operator C that acentral-office operator C has again plugged in on the trunk-wires andthat another connection is desired, and she plugs in again on theterminals of the trunking-wires, as shown in Fig. 3, and operates herlistening-key, as illustrated in Fig. 3, ascertaining from the otheroperator what subscriber is wanted now, and proceeds to make theconnection with the other subscriber wanted, as heretofore explained andillustrated.

Let us suppose that the subscriber B wanted is the first one to indicateto the central office that he is through talking and desires tobedisconected, as indicated in Fig. 7. The central-office operator 0disconnects her two switch-plugs from said subscribers terminals andfrom the terminals of the trunk-wires. This disconnection would not putout the lamps 32 at the central office 0 and would light lamp 55 atcentral office C indicating that another connection was desired, all asillustrated in Fig. 2, and would not therefore indicate to thecentral-office operator 0 that the subscribers are through talking andthat disconnection is desired To accomplish this and to enablecentraloffice operator C to signal central-office operator Of thatsubscriber B is through conversing, the centraLoffice operator 0 touchesthe key 59, connected with the line-wire 58. This throws the current ofthe grounded battery 54 on the trunking-wires t t and line-wire 57 overthe following route: from one pole of battery 54, through key 59, wire58, said current dividing at this point,one part of said current goingthrough the line-wire 57 through the relay 49, to ground, and back tothe other pole of the battery 54. This current passing through the relay49 lifts the armature thereof, Fig. 7, breaking the circuit of thebattery 54 through the incandescent lamp 55 by way of said armature andits lower contact, thus extinguishing the lamp 55. The other part of thecurrent from the battery 54, dividing at the wire 58, passes to thetrunk-wires it, to the central oflice-O, and travels down the wire 37,through the armature 38 of the magnet 29, to the front contact of saidmagnet, Fig. 7, through the relay 35,

r to ground, and returns to the other pole of the battery 54. Thiscurrent so passing through the relay draws up the armature thereofagainst its front contact. The armature 34 of the relay 35 in so doingbreaks contact with the wire 27, and therefore puts out the incandescentlamps 32 at central oflice Q, breaking the circuit of said incandescentlamps between Said armature and said wire 27, so that the central=officeoperator C by touching the key 59, signals the central office 0 todisconnect, the signal, Central-office operators (0) plug in and lightsout, meaning Disconnect.

When the central off1ce operator 0 disconnects'her plug in response tothe signal sent her, the circuit of the magnet 29 is broken be tween thewire 27 and the said plug. i Therefore the magnet 29 becomes deenergizedand allows its armature 38 to drop against its back contact, throwingthe battery on the trunkwires, as heretofore explained and shown.

To prevent the armature of the relay 35 from dropping back again awayfrom its front contact as soon as the key 59 is released bycentral-office operator C there is provided an arrangement whereby thesaid armature is held in the position placed by the current from thebattery 40, so as to keep the lamps 32 from lighting aftercentral-office operators (0 key is released.

lf operator 0 did not observe the lamps 32 go out and immediately lightagain, she would naturally suppose, from seeing them still lighted, thatthe operator C had not disconnected, and thus a false signal would begiven operator O. To obviate this, there is provided the arrangementjust referred to, which arrangem ent is specifically as follows Thefront contact of the relay 35 is oonnectedwith one pole of the battery40. The current from said battery 40 passes to the said front contact,to the armature of said relay 35 when against it, to the wire 37 as faras the armature 38 of the magnet 29, and by way of the front contact ofsaid magnet 29, through the relay 35, to ,the other pole of saidbattery. This circuit holds the armature 34 of the relay 35 against itsfront contact, after it is once placed in this position, andcentral-oflice operators (O) plug has not been disconnected. Thecentral-office operator C, by-withdrawing her plug from thetrunking-terminals,breaks the circuit which holds the armature 34 of therelay 35 up against its front contact, the said circuit being brokenbetween the armature 38 and its front contact. The armature of the relay34 then resumes its original position, (shown in Fig. 1) and all theparts are in their normal condition. The closing of this local circuitfrom battery 40 through the relay 35 at the central office, Fig. 7, doesnot remove all the current of the battery 40 from the trunk-wires andline-wire 57, containing relay 49 at the receiving-office. Part of thecurrent from battery 40 still passes to the trunkwires via the frontcontact of the relay 35, its armature 34, and line'wire 37. This part ofthe current of the battery 40, passing over the trunk-wires, traversesthe line 57 and relay 49, and is sufficient to keep the armature of saidrelay in its raised position, so that when the central-office operator 0releases her key 59, the armature of said relay 49-will be maintained inthe position placed by the current from the battery 54, and thus thecircuit of the lamp will not be completed by ICC IIO

said armature touching its lower contact, as shown in Fig. 2. The lamp55, therefore, will not light when the key 59 is released and afalsesignal will not be given the operator 0 Should another operator'atcentral office 0, seeing the lamps 32 out, plug in on the terminals ofthe trunk-wires before the operator at the central office 0 haddisconnected, the lamps 32 Would not be lighted by the second operator 0so plugging in, because the lamps 32 cannot be lighted again until thearma ture 34 of the relay 35 resumes its normal position and leaves itsfront contact, and this cannot be effected-until disconnection has beenmade by central-offi ce operator O. The second operator 0, who has thusplugged in upon the trunking-terminals, knows that the lines are notclear, for thelamps 32 do not light when the trunking-terminals areplugged in upon, as they should. The second operator O therefore plugsin upon the terminals'of some other trunkwires whose lamps 32 are notlighted.

Having fully set forth our invention, what we desire to claim, andsecure by Letters Patent of the United States, is

l. Atelephone trunking system comprising trunk-Wires, appliancesconnecting subscribers thereto, signaling devices at the sending end ofsaid trunk-wires, a circuit and source of electrical energy for saidsignaling devices, which circuit is controlled by the ap pliances inconnecting subscribers to and disconnecting them from said trunk-Wires,a circuit leading from the sending-oflice to the receiving-oflice, amagnet in the first-mentioned circuit governing the second-mentionedcircuit, and a signaling device at the receiving-oflice controlled bysaid second circuit.

2. A telephone trunking system comprising trunk-Wires, appliancesconnecting subscribers thereto, signaling devices at the sending end ofsaid trunk-Wires, a circuit and source of electrical energy for saidsignaling devices, which circuit is controlled by the appliances inconnecting subscribers to and disconnecting them from said trunk-Wires,a circuit leading from the sending-oflice to the receiving-ofiice, whichcircuit is governed by said appliances, a source of electrical energynormally energizing said latter circuit, a signaling device at thereceiving-office, and a relayin the latter-mentioned circuitgoverning'the circuit of the signaling device at the receiving-office.

3. A telephone trunking system comprising trunk-wires, appliancesconnecting subscribers thereto, signaling devices at the sending end ofsaid trunk-Wires, a circuit and source of electrical energy for saidsignaling de- 'vices, Which circuit is controlled by the appliances inconnecting subscribers to and disconnecting them from said trunk-wires,a circuit leading from the sending-office to the receiving-office andgoverned by said appliances, a source of electrical energy normallyconnected to said latter circuit, a magnet in the firstunentionedcircuit governing the latter circuit, a signaling device at thereceiving-office, and a relay in said latter circuit at the receivingend of the trunk-wires and governing the circuit of the latter-mentionedsignaling device.

4. A telephone trunking system comprising trunk-Wires, appliancesconnecting subscrib ers thereto, signaling devices at the sending end ofsaid trunk-Wires, a circuit leading from the sending-office to thereceiving-olfice and governed by the appliances in connectingsubscribers to and disconnecting them from said trunk-wires, a signalingdevice at the receiving-office, a local circuit therefor, a magnet inthe circuit leading from the sending to the receiving end of thetrunk-wires and controlling said local circuit, and contact devices forsaid local circuit, adapted to be forced apart by the insertion of thesubscriber-connecting appliances at the receiving-office.

5. A telephone trunking system comprising trunk-Wires, appliancesconnecting subscribers thereto, signaling devices at the sending end ofsaid trunk-wires, a circuit and source of electrical energy for saidsignaling devices, which circuit is controlled by the appliances inconnecting subscribers to and disconnecting them from said trunk-Wires,a circuit leading from the sending-office to the 'receiving-office andgoverned by said appliances, a relay at the receiving end in thelatter-mentioned circuit, and a local circuit controlled therebycontaining a source of electrical energy, a sigaling device and contactdevices for said local circuit, which contact devices are adapted to beforced apart by the insertion of the subscriber-001mecting appliances atthe receiving-office.

6. A telephone trunking system comprising trunk-wires, appliancesconnecting subscribers thereto, signaling devices at the sending end ofsaid trunk-wires, a circuit and source of electrical energy for saidsignaling devices, which circuit is controlled by the appliances inconnecting subscribers to and disconnecting them from said trunk-wires,a circuit leading from the sending-office to the receiving-office andgoverned by said appliances, a relay at the receiving end of thelatter-mentioned circuit, and a local circuit c011- trolled thereby,containing a source of electrical energy and signaling device, the saidlocal circuit being established by the subscriber-connectin g appliancesat the receiving-office.

7. A telephone trunking system comprising trunkwvires, appliancesconnecting subscribers thereto, signaling devices at the sending end ofsaid trunk-wires, a circuit and source of electrical energy for' saidsignaling devices, which circuit is controlled by the appliances inconnecting subscribers to and disconnecting them from said trunkwires',a circuit leading from the sending-office to the receiving-office andgoverned by said appliances, a

branch of said local circuit being established by thesubscriber-connecting appliances.

8; Atelephone trunking system comprising trunk-wires, appliancesconnecting subscribers thereto, signaling devices at the sending end ofsaid trunk-wires, a circuit and source of electrical energy for saidsignaling devices, 7

which circuit is controlled by the appliances in connecting subscribersto and disconnecting them from said trunk-Wires, a circuit leading fromthe sending-office to the receiving-oifice and governed by saidappliances, a relay at the receiving end of the latter-mentionedcircuit, a local circuit controlled thereby and containing a source ofelectrical energy and a signaling device, the said local circuit beingestablished by the subscriberconnecting appliances, a magnet in saidlocal circuit, and a shunt controlled thereby and adapted toshort-circuit the armature of said relay after the closing of said localcircuit by said armature.

9. A telephone trunking system comprising trunk-Wires, appliancesconnecting subscribers thereto, signaling devices at the sending end ofsaid trunk-wires, a circuit and source of electrical energy for saidsignaling devices, which circuit is controlled by the appliances inconnecting subscribers to and disconnecting them from said trunk-wires,a circuit leading from the sending-office to the receivingofiice andgoverned by said appliances, a relay at the receiving end of thelatter-mentioned circuit, a local circuit controlled thereby having twobranches, one connected to each contact of said relay, a source ofelectrical energy and a signaling device in said branches, contacts forone of said branches adapted to be forced apart by the twosubscriber-connecting appliances, the other branch of said local circuitbeing established by the subscriberconnecting appliances, a magnet inthe latter branch of said local circuit, and a shunt controlled therebyand adapted to short-circuit the armature of said relay after theclosing of said branch by said armature.

10. A telephone trunking system comprising trunk-wires, appliancesconnecting subscribers thereto, signaling devices at the sending end ofsaid trunk-Wires, a circuit and source of electrical energy for saidsignaling devices, which circuit is controlled by the appliances inconnecting subscribers to and disconnecting them from said trunk-wires,a

-magnet in said circuit, a circuit leading from the sending-office tothe receiving-office and governed by said magnet, a source of electricalenergy normally connected to said latter circuit by way of the backcontact of said magnet, a second magnet connected to the front contactthereof and controlling the circuit of the signaling devices, a relay atthe receiving end of the circuit leading from the sending-office, alocalcircuit controlled thereby and having a signaling device and source ofelectrical energy connected therewith and adapted to be made and brokenby the subscriber-connecting appliances, a key, and

suitable battery connections at the receivingoffice adapted to be placedin communication With the circuit leading from the sending to thereceiving office.

11. A telephone trunking system comprising trunk-wires, appliancesconnecting subscribers thereto, signaling devices at the sending end ofsaid trunk-Wires, a circuit and source of electrical energy for saidsignaling devices, which circuit is controlled by the appliances inconnecting subscribers to and disconnecting them. from said trunk-Wires,a

magnet in said circuit, a circuit leading from.

the sending-office to the receiving-oflice and governed by said magnet,a source of electrical energy normally connected to said latter circuitby Way of the back contact of said magnet, a relay connected to thefront contact thereof and controlling the circuit of said signalingdevices and the circuit leading from the sending to the receivingoffice, a local circuit from said last-mentioned source of electricalenergy through said relay, said local circuit being governed by saidmagnet and relay, a relay at the receiving end of the circuit leadingfrom the sending-office, a local circuit controlled thereby having asignaling device and source of electrical energy connected therewith andadapted to be made and broken by the subscriber-connecting appliances,akey, and suitable battery connections at the receiving-office adapted tobe placed in communication with the circuit leading from the sending tothe receiving office. r

In Witness whereof We have hereunto set our hands and affixed our seals.

GEO. F. DURANT. L. s.] WILLIAM WV. DEAN. L. WM. A. OI-IILDS. L. s.

lVitnesses for Geo. F. Durant and William 7. Dean:

CHAS. J. BYRNE, W. E. HARKNESS.

NVitnesses for l/Vni. A. Childs:

CHARLES SHAW, J. H. ADAMS.

IIO

